Abstract Parkinson's Disease (PD) is defined by the accumulation of alpha-synuclein (Asyn) fibrils in neuronal cytoplasmic and neuritic inclusions known as Lewy bodies and Lewy neurites. The role of Asyn in pathogenesis is supported by the identification of dominant mutations in the gene encoding Asyn (SNCA) in rare familial versions of PD. PD progression, particularly the development of dementia in PD, is associated with more widespread deposition of Asyn throughout the brain, including neocortex. Multiple therapeutic approaches targeting Asyn accumulation are being pursued. A leading priority is to develop a PET imaging agent that can quantify the deposition of Asyn in living individuals, as a biomarker for target engagement in clinical studies. An Asyn PET imaging agent would also improve the accuracy of diagnosis for PD, and provide a biomarker for disease progression. We developed a new screening approach to identify novel compounds that can be pursued as leads for the development of an Asyn imaging agent. This new approach uses fluorescence measurements to identify a subset of natively fluorescent compounds in a commercial library. We then use fluorescence measurements to screen natively fluorescent compounds for binding Asyn fibrils in vitro followed by assessment of whether compounds bind to Asyn-containing Lewy bodies in postmortem PD brain tissue sections. A final step is to determine whether compounds selectively bind to Lewy bodies but do not bind to amyloid plaques or neurofibrillary tangles in postmortem brain tissue sections. The project will use this approach to screen 5000 fluorescent compounds. Compounds found to have the desired properties will be radiolabeled with tritium in order to further characterize their binding properties using radioligand binding assays and autoradiography. The compounds identified in the project can be used as leads in further studies to develop an Asyn imaging agent. Results from the project will also enable further optimization of this new screening approach to identify compounds with the binding properties needed for an imaging agent.